I am trying to build a simple transmitter and receiver in simulink. Output of random number generator multiplied with PN generator. Then, after bpsk modulation and raised cosine pulse shaping it is fed to awgn channel. I need to know the parameters for this design and ways to reduce BER.

 

I have some practical suggestions but those will come later in the implementation. Since you do not have sufficient information to anticipate the transmitted message you need to make sure the transmitted signal has sufficient signal power to overcome the noise. You need repetition without a request for re-transmission and you need some form of acknowledgement from the receiver. Next you need to build the best damn receivers money can buy to pull weak signals out of the rug. Then you need to have resonant and directional antennas with rotors to maximize the effectiveness of whatever signal power you have. Last you need some good DSP software, like WSJT, to work with whatever coding scheme you come up with. Google FSK441 and JT65 for examples of weak signal modes that work well for Meteor Scatter and EME (Earth Moon Earth) communications.

 

What parameters are you neediing to know? What work have you accomplished to date on this? What are your constraints? What aspects are you trying to focus on?